The present invention constitutes a new and distinct variety of Hydrangea plant, which was developed by artificially pollinating an unnamed seedling(not patent in the US) with an unnamed seedling (not patent in the US). The two parents were crossed in the spring of 2005 and the resulting seed was sown in September 2005, in a controlled glasshouse environment. Out of these seedlings one seedling was selected, as the new variety and named ‘HYDthree’. The new Hydrangea plant may be distinguished from its seed parent, an unnamed seedling, by the following combination of characteristics:                1. The unnamed seedling has a breeding background in unnamed seedlings.        2. ‘HYDthree’ has medium dome-shaped inflorescences, while the unnamed seedling has large dome-shaped inflorescences.        3. ‘HYDthree’ has pink or blue colored flowers, while the unnamed seedling has white flowers.        
The new variety may distinguished from its pollen parent, an unnamed seedling created by the same inventor, by the following combination of characteristics:                1. The unnamed seedling has a breeding background in unnamed seedlings.        2. ‘HYDthree’ has medium dome-shaped inflorescences, while the unnamed seedling has small flat inflorescences. ‘HYDthree’ has pink or blue flowers, while the unnamed seedling has red flowers.        